1. Field of the Invention
This invention relates to deposited layers of chromium, and, more particularly, to a method of making an adherent, smooth electrodeposit of chromium on a nodular cast iron substrate from a high energy efficient chromium plating path.
2. Description of the Prior Art
The use of high energy efficiency (HEEF) chromium plating processes has been hampered by the inability to obtain adequate coating adhesion and smoothness to certain basis metals. Such baths are of the types disclosed in Mitsui, J7B-33941 (September, 1978); U.S. Pat. Nos. 4,093,522; to Dillenberg, 4,234,396; to Perakh, and 4,450,050; 4,472,249 and 4,588,481 to Chessin.
Many activation treatments have been proposed for plating adherent chromium onto various substrates. For example, in order to obtain an adequate bond, as measured ASTM B 571-79, with typical chromium plating solutions, such as those using a solution of chromic acid and catalysts, such as sulfate, or sulfate in combination with various fluorides, the usual technique is to reverse or anodically etch a ferrous workpiece in the plating solution or in a separate chromium acid containing solution at a predetermined current density for a predetermined time.
A table which lists the time lengths for such an etching process is found in "Metal Finishing" 80 (5) 65-8 (1982) by C. H. Peger.
Anodic chromic acid treatments for 400 stainless steel alloys and for low and high carbon steels is disclosed in "48th Metal Finishing Guidebook-Directory" 78, 188-202 (1980) by A. Logozzo. Also recommended are cathodic treatments in sulfuric-fluoride solutions for 300 stainless, for nickel alloys and for cast iron.
Brune and McEnally in "Plating" 42, 1127-32 (1955) describe the use of magnesium sulfate acid anodic etch solution for preparing ferrous parts for plating. Similarly, ASTM Specification B-242-49T suggests the application of an anodic etch using a sulfuric acid solution containing sodium sulfate. ASTM B177-68 described the use of sulfuric acid or chromic acid as activators for chromium electroplating on steel for engineering use.
Chessin in U.S. Pat. No. 4,450,050 described an activation pretreatment for bonding high efficiency chromium electrodeposits on a metal substrate which is characterized by the step of first plating the substrate metal with iron or an iron alloy from an iron salt containing bath.
Hermann, in U.S. Pat. No. 4,416,758, activates metal substrates in an aqueous alkaline cyanide containing solution using current which is periodically reversed, followed by rinsing and chromium plating.
McMullen et al, in U.S. Pat. No. 4,585,530, describes an activation process using a substantially neutral solution of an alkali metal sulfate.
These and other activation solutions and procedures are intended to provide an adherent electrodeposit of chromium onto basis metal substrates. However, in the case of ferrous metal substrate, e.g. cast iron, which have a nodular or spheroidal structure, the activation or etching treatment still leaves a relatively non-uniform surface. Electrodeposition of chromium thereon thus produces a roughened surface layer. Furthermore, when such chromium layers are electrodeposited from a high energy efficient (HEEF-40 or HEEF-25) baths, such as the commercial HEEF baths based on U.S. Pat. Nos. 4,472,249 and 4,558,481, deposit builds up on the nodules and underlying portions of the substrate, producing a layer having a severely roughened surface.
Accordingly, it is an object of this invention to provide a method of producing an adherent, smooth deposit of chromium on a nodular or spheroidal ferrous metal substrate, such as cast iron, particularly an electrodeposit of chromium thereon from a high energy efficient (HEEF) plating bath.
Another object is to provide adherent, smooth deposits of chromium on such substrates using a wide range of different activation treatments.
A feature of the present invention is the application of an ultrasonic treatment on an activated nodular or spheroidal cast iron substrate whereby it can receive an adherent, smooth deposit of chromium thereon, particularly from a HEEF bath.
Another feature herein is that an ultrasonic treatment is effective to provide adherent, smooth deposits on such substrates with HEEF and other baths, using a wide range of different activation treatments.